Making Ethanol from Wood Chips

Making Ethanol from Wood Chips

Mascoma is focusing on improving the first steps of the process–pretreating raw materials and converting cellulose into sugars–which South says are key to reducing costs. In the conventional pretreatment step, materials such as wood chips are soaked in a dilute solution of sulfuric acid and then heated. This breaks down complex lignin structures that form a “shield” around the cellulose, says Charles Wyman, Mascoma co-founder and professor of chemical and environmental engineering at the University of California, in Riverside. Wyman’s research has analyzed the mechanisms involved in this process, helping the company optimize this step. Mascoma has also developed technology for improving the next step: breaking down the now accessible cellulose into sugars by using enzymes produced by organisms. In the latter part of the process, these sugars are fermented to make ethanol.

Wyman estimates that the company’s technology could produce ethanol for about the same cost as producing ethanol from corn, and eventually for less money. This would be a significant improvement over other technology. A cost analysis at an NREL pilot plant, for example, suggests that it would cost more than two dollars a gallon to make cellulosic ethanol–about double the cost of making corn ethanol. But even NREL researchers are confident that this cost will be cut in half and meet corn-ethanol costs within six years, Douglas says.

Producing enough ethanol to replace a significant fraction of gasoline consumption is still many years away, however. It will require further improving both the technology and the industrial processes, including the challenges that go with handling large amounts of bulky biomass. “We are definitely not there yet,” says MIT’s Stephanopoulos. “Processes today are clearly uneconomical.”

But Douglas says researchers are optimistic that continued funding and the application of new tools will make widespread cellulosic ethanol possible: “The pathways are pretty clear.”